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A polyploid is an organism that has three or more sets of chromosomes (opposed to the two sets found in many eukaryotic species). Allopolyploids are species which are polyploids that are also a hybrid of two species.

One common allopolyploid is the crop species Triticale. This hybrid species is made by mating a diploid rye plant with a tetraploid wheat. The rye has 14 chromosomes, producing a gamete with seven chromosomes. The wheat has 28 chromosomes, producing a gamete with 14 chromosomes.

The hybrid seed is allowed to germinate. However, before the plant is allowed to produce seeds, it is treated with the chemical colchicine, which causes the chromosomes to double in the germ cells.

What is the primary reason the plants are treated with colchicine?

A

Plants with higher ploidy numbers tend to be larger and therefore are more useful as crops. By doubling the chromosomes in the gametes, it makes the next generation much larger and more useful as foodstuffs.

B

Doubling the chromosome number in the gametes causes the plants to produce many more seeds, thereby allowing more of the hybrid crop to be produced much more quickly.

C

Doubling the chromosomes prevents unbalanced gametes that would result if the original hybrid plant underwent meiosis.

D

By doubling the chromosome number, the effects of recessive genes can be reduced.

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